Although this thread is a little older, I thought I would throw in my two cents regarding quiet generators. I'm the editor of Volt Magazine, which focuses on generators and power requirements.
The posters here made some very good points and described inverter generators accurately, but no one addressed what sound rating a quiet generator should be rated at. When it comes to noise output, generators are rated on what is called DBA - which is levels of Decibels on the A scale of sound. For a generator to be considered quiet it needs to have a DBA level of below 56 and the closer to 50 the better. The quietest generator I know of is a Honda that comes in at 49 dba. To put this in perspective, human conversation takes place at 60 to 65 dba.
The second consideration when you are buying any generator is that it is compliant with both CARB rules which stands for California Air Resources Board - as well as EPA rules. The goverment website it Air Resources Board - Homepage
You can read a lot more on which models run quiet etc and what to look for on our website at Volt Magazine's Quiet Generator Guide | Finding the best quiet generators
Hope that helps everyone.